WASHINGTON - An intensifying debate over Judge Brett Kavanaugh, a front-runner in President Donald Trump's search for a Supreme Court nominee, gripped Republicans Tuesday, with conservative critics highlighting past rulings and his links to GOP leaders while his allies - including inside the White House - forcefully defended him.

The sparring over Kavanaugh, one of four federal appeals court judges who met with the president Monday, underscored the challenges facing Trump as he races to pick a successor to retiring Justice Anthony Kennedy by his own July 9 deadline. Even as Trump mulls a shortlist that has been carefully cultivated by influential Republican lawyers, frictions in the conservative legal community and on Capitol Hill threaten to disrupt the search process.

The political moment for Trump remained fragile as a president devoted to his base weighed what a Kavanaugh selection could mean for him, unfolding amid a flurry of op-eds and phone calls praising the 53-year-old judge as well as a clamor from those who see him as out of step on health care and abortion, or too tied to George W. Bush's White House.

"You hear the rumbling because if you've been part of the establishment for a long time, you're suspect," veteran conservative organizer Richard Viguerie said in an interview. "Kavanaugh carries that baggage."

Trump advisers said Tuesday that the president was aware of the squabbling and closely monitoring news coverage of his interviews, but they cautioned that he has not been swayed by a particular voice.

The president, however, has asked aides about Kavanaugh's opinions on health care that have frustrated some conservatives, according to two people close to the president who were not authorized to speak publicly. They added that Trump had pored over news articles that have spotlighted Kavanaugh's history with George W. Bush - part of a powerful political family that has vocally opposed Trump - but did not see it as a fatal strike against him.

Trump has also spoken by phone with Sen. Rand Paul, R-Ky., this week, according to three people briefed on the call who were not authorized to discuss it publicly. Paul and his advisers had quietly conveyed their concerns about Kavanaugh to the White House in recent days, citing his decisions on health care. Since Republicans hold a narrow 51-seat majority in the Senate, losing just one GOP vote could jeopardize a nominee.

MSNBC's Nicolle Wallace, a former Bush adviser, noted on her afternoon program Tuesday that former Bush officials were being careful to not be too effusive about Kavanaugh, or else risk hurting their former colleague's chances.

"This is the whisper campaign that's out there trying to destroy Kavanaugh and it could be legit," syndicated radio-show host Rush Limbaugh told his listeners Monday. "The long knives are out from people from all sides of the aisle, folks."

Kavanaugh, 53, has a long history in Washington, having helped investigate President Bill Clinton as part of independent counsel Kenneth Starr's team and then serving as a close aide to Bush before joining the U.S. Court of Appeals for the District of Columbia Circuit in 2006.

The rush of scrutiny and objections have vexed Kavanaugh supporters, who days ago viewed him as one of the strongest prospects due to his past tenure as a Kennedy clerk and deep support among veteran Republican attorneys - and given a sudden jolt of hope to supporters of other contenders for the bench.

"A bunch of haters have come out against Judge Kavanaugh," wrote David Lat, the founding editor of the legal website Above the Law. "The attacks lack merit, especially the ones from the right."

The questions have come from some social conservatives, a group Trump has relied on for continued and fervent support after promising during the 2016 campaign to appoint justices who would overturn Roe v. Wade, the landmark 1973 ruling that legalized abortion nationwide.

Jim Bopp, a prominent social conservative and attorney, has expressed wariness about Kavanaugh's handling of certain cases in a letter to Trump, according to a report by The National Law Journal. When reached for comment Tuesday, Bopp said his letter was not meant to oppose any candidate but "simply to prompt a discussion about who's the best person," and declined to talk about Kavanaugh.

Kavanaugh's critics have pointed to a recent case involving a pregnant immigrant teenager in federal custody as reason to doubt his conservatism on the abortion front.

He voted against the teenager, who was seeking immediate access to abortion services, and noted the government's "permissible interest" in "favoring fetal life," but he did not go as far as another District Circuit judge, Karen Henderson, who said the undocumented teen had no constitutional right to an elective abortion.

Shannen Coffin, former deputy assistant attorney general during the Bush administration, said, "It's a bit baffling to me that conservatives would find reason for alarm in that case when he was a dissenting judge . . . He's bound by Supreme Court precedent."

A 2016 case over the contraceptive mandate in President Barack Obama's health-care law has also drawn attention. Kavanaugh sided with the group Priests for Life, but in his opinion he wrote that Supreme Court precedent "strongly suggests that the Government has a compelling interest in facilitating access to contraception," but that there were less "restrictive means of furthering" that interest.

Separately, in a 2011 challenge to Obama's health-care law, Kavanaugh dissented from a District Circuit decision upholding Obamacare, but he did so for technical and jurisdictional reasons instead of declaring the law unconstitutional, as ideological purists would have preferred.

Kavanaugh, a Yale Law School graduate who grew up in Bethesda, Maryland, has also seen his personal biography lauded and criticized, with some Republicans seeing a reliable conservative and others seeing a political insider.

White House counsel Donald McGahn, who is coordinating the candidate interviews for Trump, has been unpersuaded by Kavanaugh's opponents and has spoken repeatedly and reassuringly about his credentials with top Republicans, according to three people briefed on those discussions.

But McGahn's ability to stave off jabs at Kavanaugh could be tested in the coming days as the debate leapfrogs from Washington think tanks and law firms to the turbulent world of conservative media.

The White House communications team, which set up a political war room Monday to bolster the eventual nominee, has been mum about Kavanaugh since the president has yet to make a decision, leaving the debate to play out largely without White House involvement.

William Kristol, editor at large of The Weekly Standard magazine, a conservative magazine, dismissed the back and forth as "what usually happens when you have an opening on the court. The small world of conservative lawyers, law clerks, and potential judges come out with their judgments and their loyalties."

Some Trump supporters are torn. "Kavanaugh is clearly the best choice. But Barrett would be the most fun," conservative commentator Ann Coulter tweeted Tuesday, referring to federal Judge Amy Coney Barrett, another finalist for the high court who clashed with Senate Democrats last year during her confirmation hearing when they asked questions about her Catholic faith.

Coney Barrett's confirmation fight also propelled the Notre Dame Law School alumna and professor to a certain legal stardom among conservatives and many Kavanaugh critics have cited her as their favorite due to that experience and what they described as an appealing profile for a court full of Ivy Leage graduates.

Along with Kavanaugh and Coney Barrett, Trump met Monday with federal appeals court judges Amul Thapar and Raymond Kethledge, according to three people briefed on the meetings who spoke on the condition of anonymity because they were not authorized to speak publicly.

Sen. Mike Lee, R-Utah, a long-shot candidate for the court, also spoke with Trump by phone. "It was in a nominee capacity," Lee spokesman Conn Carroll said of the president's conversation with Lee, who is a member of the Senate Judiciary Committee, which will vet Trump's nominee. Lee's interview with Trump was first reported by the Deseret News.

White House spokesman Raj Shah also confirmed that Trump spoke on the phone with Lee, although Shah did not characterize it as an interview.

Two others on Trump's shortlist are federal appeals court Judge Thomas Hardiman and Judge Joan Larsen, according to Trump advisers. The White House said the president spoke to three potential Supreme Court nominees Tuesday but did not disclose their names.

As Trump reviewed his shortlist, advocates for finalists were busy Tuesday talking to White House officials and other allies of the president, still believing that the process remains fluid and potentially upended, should Kavanaugh fall out of favor at some point this week.

Kethledge - another former Kennedy clerk whose meeting Monday with Trump went favorably, according to three people briefed on the session - saw "Lead Yourself First," his co-written book on leadership, circulated around conservative legal circles.

"He's somebody who could come from outside of Washington," former Michigan senator Spencer Abraham, R, said in an interview. Abraham, a friend of Kethledge, said "the court could use some diversity in terms of background." Kethledge is a graduate of the University of Michigan Law School.

"Allison Eid," a federal judge in Colorado, "is my favorite partly because I know her and she used to work for me," former education secretary Bill Bennett said. "I've floated her on TV and elsewhere."

The well-connected orbit of Senate Majority Leader Mitch McConnell, R-Ky., continued Monday to talk up Thapar. And Hardiman was boosted by a friend, former Pennsylvania Rick Santorum, who made phone calls on his behalf.

"He's the most confirmable," Santorum said in an interview, describing his pitch. "You look at his background" - Hardiman drove a taxi to help pay for law school - "and you see somebody who's not just a white-shoe lawyer guy."